Internal short detection and mitigation in batteries

ABSTRACT

Devices, systems, and techniques for identifying a dendrite material within a battery. The method comprising receiving, by a battery management system, an output from sensing circuitry within the battery indicative of a first voltage level, detecting, by the battery management system, a change from the first voltage level to a second voltage level that is indicative of an internal short within a sensing sheet, determining by the battery management system, a resistance and a two-dimensional position of the internal short within the sensing sheet, and identifying, by the battery management system, a dendrite material based on the resistance of the internal short.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.14/972,957, filed Dec. 17, 2015, the entire contents of which isincorporated herein by reference.

FIELD

Embodiments of the invention generally relate to batteries and, moreparticularly, to the detection and mitigation of internal shorts causedby dendrite formation in a battery.

BACKGROUND

Rechargeable lithium batteries are attractive energy storage devices forportable electric and electronic devices and electric andhybrid-electric vehicles because of their high specific energy comparedto other electrochemical energy storage devices. A typical lithium cellcontains a negative electrode, a positive electrode, and a separatorlocated between the negative and positive electrodes. Both electrodescontain active materials that react with lithium reversibly. In somecases, the negative electrode may include lithium metal, which can beelectrochemically dissolved and deposited reversibly. The separatorcontains an electrolyte with a lithium cation, and serves as a physicalbarrier between the electrodes such that none of the electrodes areelectrically connected within the cell.

Typically, during charging, there is generation of electrons at thepositive electrode and consumption of an equal amount of electrons atthe negative electrode. During discharging, opposite reactions occur.

Lithium dendrites (needle- or tree-like growths) may be formed duringrepeated charge/discharge cycles of a battery. The dendrites canpenetrate through the separator region of the battery and cause aninternal short between the negative and positive electrodes. The rapiddischarge caused by the short can release excessive heat within thebattery causing damage to the battery.

SUMMARY

Traditional approaches to addressing dendrite formation have includedmodification of the electrolyte and electrolyte solvent, and modifyingthe surface morphologies of the electrodes. Despite these ongoingefforts, the formation of dendrites continues to occur. Non-uniform(re)-deposition of lithium during the charge/discharge cycles of thebattery often results in dendrite formation. Thus, there is a need for asystem and method for the detection and mitigation of dendrites within arechargeable battery prior to the formation of an internal short betweenthe positive and negative electrodes.

A summary of certain embodiments disclosed herein is set forth below. Itshould be understood that these aspects are presented merely to providethe reader with a brief summary of these certain embodiments and thatthese aspects are not intended to limit the scope of this disclosure.Indeed, this disclosure may encompass a variety of aspects that may notbe set forth below.

One embodiment relates to a method of detecting and treating theformation of lithium dendrites in a battery, and in particular, to amethod for identifying a dendrite material in the battery. In oneexample, the method for identifying a dendrite material in the batteryincludes receiving, by a battery management system, an output fromsensing circuitry within a battery cell indicative of a first voltagelevel, detecting a change from the first voltage level to a secondvoltage level that is indicative of an internal short between anelectrode and a sensing sheet, determining, a resistance and atwo-dimensional position of the internal short on the sensing sheet, andidentifying a dendrite material based on the resistance of the internalshort.

Another embodiment provides a battery. In one example, the batterycomprises an anode, a cathode, an electrically insulating separator, andsensing circuitry. The electrically insulating separator has a sensingsheet and located between the anode and the cathode. The electricallyinsulating separator electrically insulates the anode from the cathode,and includes at least three sensing tabs located at the periphery of thesensing sheet. The sensing circuitry is electrically connected to eachof the three or more sensing tabs and configured to determine at leastone of a resistance, a current, or a voltage at each of the three ormore sensing tabs. The sensing circuitry outputs an indication of the atleast one of the resistance, the current, or the voltage at each of thethree or more sensing tabs.

Yet another embodiment provides a system comprising a battery and abattery management system. In one example, the battery has an anode, acathode, an electrically insulating separator, and a sensing circuitry.The electrically insulating separator has a sensing sheet and locatedbetween the anode and the cathode. The electrically insulating separatorelectrically insulates the anode from the cathode, and the sensing sheetincludes three or more sensing tabs located at the periphery of thesensing sheet. The sensing circuitry is electrically connected to eachof the three or more sensing tabs and configured to determine at leastone of a resistance, a current, or a voltage at each of the three ormore sensing tabs. The sensing circuitry outputs an indication of the atleast one of the resistance, the current, or the voltage at each of thethree or more sensing tabs. The battery management system iscommunicatively connected to the battery and configured to receive theoutput from the sensing circuitry, and determine a resistance and atwo-dimensional position of the internal short on the sensing sheetbased on the output from the sensing circuitry.

The details of one or more features, aspects, implementations, andadvantages of this disclosure are set forth in the accompanyingdrawings, the detailed description, and the claims below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a battery cell and sensingcircuitry, in accordance with one embodiment.

FIG. 2 is a schematic illustration of a battery cell, in accordance withone embodiment.

FIG. 3A is a schematic illustration of a battery cell in accordance withanother embodiment.

FIG. 3B is a schematic illustration of a battery cell, in accordancewith certain embodiments.

FIG. 4 is a schematic illustration of a sensing sheet within a batterycell, in accordance with one embodiment.

FIGS. 5A and 5B are schematic illustrations of a battery systemincluding a battery cell and a battery management system, in accordancewith some embodiments.

FIG. 6 is a schematic illustration of a battery system including abattery sensing sheet and battery management system, in accordance withone embodiment.

FIG. 7 is a schematic illustration of a sensing sheet within a battery,in accordance with one embodiment.

FIG. 8 is a schematic illustration of a sensing sheet within a battery,in accordance with one embodiment.

FIG. 9 is a flowchart illustrating an example method of identifying thepresence of an internal short in a battery, in accordance with oneembodiment.

FIG. 10 is a flowchart illustrating an example method of identifying andtreating the presence of an internal short in a battery, in accordancewith one embodiment.

DETAILED DESCRIPTION

One or more specific embodiments will be described below. Variousmodifications to the described embodiments will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to other embodiments and applications without departing fromthe spirit and scope of the described embodiments. Thus, the describedembodiments are not limited to the embodiments shown, but are to beaccorded the widest scope consistent with the principles and featuresdisclosed herein.

An embodiment of a battery cell 100 is shown in FIG. 1. In the exampleillustrated, the battery cell 100 includes an anode tab 110, an anode120, a separator 130, sensing tabs 140A, 140B, and 140N (collectively“sensing tabs 140”), a cathode 150, a cathode tab 160, and sensingcircuitry 170. In some examples, the separator 130 may be anelectrically insulating separator. In some embodiments, the electricallyinsulating separator comprises a porous polymeric film. For ease ofunderstanding the sensing tabs 140 are illustrated as positioned at theedge of the separator 130. It should be understood that in someembodiments the sensing tabs 140 are connected to a single sensing sheet(not shown) located within the separator 130.

In various embodiments the sensing circuitry 170 may be configured tomeasure parameters such as at least one of voltage, current, orresistance between a combination of the anode 120, a sensing sheetwithin the separator 130, and the cathode 150. The sensing circuitry 170may also be configured to communicate with a device external to thebattery cell 100. For example, the sensing circuitry 170 may beconfigured to communicate with a battery management system. In someexamples, the sensing circuitry 170 may communicate with a batterymanagement system external to the battery cell 100 by adjusting thevoltage across the anode tab 110 and the cathode tab 160.

The battery cell 100 has a stacked architecture, which is best seen byreference to FIG. 2. FIG. 2 illustrates a battery cell 200 which issimilar to the battery cell 100. In the example illustrated, the batterycell 200 includes a stack of components 205. The stack of components 205includes an anode current collector 210, an anode current collector tab220 attached to the anode current collector 210, and an anode 230. Thebattery cell 200 also includes a first separator 240 (e.g., a firstelectrically insulating separator), and a sensing sheet 250. The sensingsheet 250 has a sensing tab 255. A second separator 260 (e.g., a secondelectrically insulating separator) is located adjacent to the sensingsheet 250, opposite the first separator 240, such that the sensing sheet250 is positioned between the first separator 240 and the secondseparator 260. The battery cell 200 also includes a cathode 270, acathode current collector 280, and a cathode current collector tab 290attached to the cathode current collector 280. In the illustratedexample of FIG. 2, the first separator 240 is thinner than the secondseparator 260. In this way, the battery cell 200 is configured to detecta metallic dendrite growing from the anode 230 early in its formationthus minimizing its ability to cause damage within the battery cell 200.

Two embodiments of a battery cell are shown in FIGS. 3A and 3B. FIG. 3Aillustrates a battery cell 300 that includes an anode current collector320 that has an anode current collector tab 310, The anode currentcollector 320 is positioned adjacent to an anode 330. A first separator340 is positioned adjacent the anode 330 and a sensing sheet 350, havinga sensing tab 355, is positioned adjacent to the separator 240. A secondseparator 360 is positioned adjacent to the sensing sheet 350. Thus, thesensing sheet 350 is positioned between the first and second separators340 and 360. The battery cell 300 also includes a cathode 370 and acathode current collector 380, which has a cathode current collector tab390. FIG. 3B illustrates a battery cell 395. The battery cell 395includes a stack of components 397. The battery cell 300 and the batterycell 395 are the same except that instead of a first separator 340 and asecond separator 360, the battery cell 395 includes a separator 361between the sensing sheet 350 and the cathode 370, which is similar tosecond separator 360 as described in FIG. 3A. In the illustrated exampleof FIG. 3A, a thickness of the first separator 340 and a thickness ofthe second separator 260 are substantially similar. In this way, thebattery cell 300 is configured to detect a dendrite formed on thecathode 270 at a time similar to a dendrite formed on the anode 230,assuming that the dendrites occur at similar times and grow at similarrates.

In the battery cells 300 and 395, the sensing sheet 350 is locatedadjacent to at least one separator. However, the sensing sheet 350 maybe located in other positions within the battery cell 300 or 395, as thecase may be. In certain embodiments, the anode 330 may include anelectrically insulating buffer layer, such as aluminum oxide (Al₂O₃),between the anode 330 and separator 340. In one embodiment, theinclusion of the electrically insulating buffer layer may allow thesensing sheet 350 to be placed adjacent to the anode 330 without aseparator 340 between the separator 340 and anode 330. It is understoodthe electrically insulating buffer layer is a safety factor layer ofanode 330. The lack of a separator (e.g., the first separator 340)between the sensing sheet 350 and the anode 330 allows the sensing sheet350 to be spatially located in closer proximity to the anode 330.Earlier detection of dendrite formation is possible with suchconfigurations because shorter dendrites may be detected when thesensing sheet 350 is closer to an electrode (e.g., the anode 330).Similarly, if early detection of dendrite formation at the cathode 370is desired the sensing sheet 350 may be similarly placed closer to thecathode 370 by placing the separator 361 between the anode 330 and thesensing sheet 350 instead of between the cathode 370 and the sensingsheet 350 as illustrated in the example of FIG. 3B. In variousembodiments the thickness dimension of the components of the batterycells 300, 395 may be for the anode current collector 320 about 10 to 15micrometers, the anode 330 about 5 to about 100 micrometers, theseparator 340 less than about 10 micrometers or in certain embodimentsabout 2 to about 3 micrometers, the sensing sheet 350 about 50 to about100 nanometers, the separator 360 about 10 to about 25 micrometers, thecathode 370 about 50 to about 100 micrometers, the cathode currentcollector 380 about 10 to about 20 micrometers.

As noted above, dendrite formation occurs during charge/dischargecycles. In the text that follows, a description of a charge/dischargecycle of battery cell 395 is provided. However, the concepts discussedalso apply to the battery cells 100, 200, and 300.

During the discharge of battery cell 395, lithium is oxidized at theanode 330 to form a lithium ion. The lithium ion migrates through theseparator 361 of the battery cell 395 to the cathode 370. Duringcharging the lithium ions return to the anode 330 and are reduced tolithium. The lithium may be deposited as lithium metal on the anode 330in the case of a lithium anode 330 or inserted into the host structurein the case of an insertion material anode 330, such as graphite, andthe process is repeated with subsequent charge and discharge cycles. Inthe case of a graphitic or other Li-insertion electrode, the lithiumcations are combined with electrons and the host material (e.g.,graphite), resulting in an increase in the degree of lithiation, or“state of charge” of the host material. For example,xLi⁺+xe³¹+C₆→Li_(x)C₆. Too high a charging current can result in Limetal deposition at the surface of the negative electrode, which in turncould lead to non-uniform deposition of lithium resulting in thedevelopment of a lithium dendrite on the surface of the anode 330.Without mitigation, as the length of the dendrite grows, the dendritecan span the separator 361 and form an internal short between the anode330 and cathode 370. The placement of a sensing sheet 350 intermediatebetween the anode 330 and the cathode 370 allows for the detection andidentification of dendrite formation prior to the dendrite forming aninternal short between the anode 330 and the cathode 370. In otherwords, the placement of the sensing sheet 350 between the anode 330 andthe cathode 370 allows for a different internal short between either theanode 330 or the cathode 370 and the sensing sheet 350, such thatdendrite formation can be detected and identified. Additionally, in someexamples, the dendrite formation may also be mitigated to prevent atypical internal short between the anode 330 and the cathode 370.

The anode 330 may comprise an oxidizable metal, such as lithium or aninsertion material that can insert Li or some other ion, such as Na, Mg,etc. The cathode 370 may comprise various materials such as sulfur orsulfur-containing materials (e.g., polyacrylonitrile-sulfur composites(PAN-S composites), lithium sulfide (Li₂S)); vanadium oxides, such asvanadium pentoxide (V₂O₅); metal fluorides, such as fluorides oftitanium, vanadium, iron, cobalt, bismuth, copper and combinationsthereof; lithium-insertion materials, such as lithium nickel manganesecobalt oxide (NMC), lithium-rich NMC, lithium nickel manganese oxide(LiNi_(0.5)Mn_(1.5)O₄), lithium-rich layered oxides, such as, lithiumcobalt oxide (LiCoO₂), lithium iron phosphate (LiFePO₄), lithiummanganese oxide (LiMn₂O₄), lithium nickel cobalt aluminum oxide (NCA),and combinations thereof The particles may further be suspended in aporous, electrically conductive matrix that includes polymeric binderand electronically conductive material such as carbon (carbon black,graphite, carbon fiber, etc.). In some examples, the cathode maycomprise an electrically conductive material having a porosity ofgreater than 80% to allow the formation and deposition/storage ofoxidation products such as lithium peroxide (Li₂O₂) or lithium sulfide,(Li₂S) in the cathode volume. The ability to deposit the oxidationproduct directly determines the maximum power obtainable from thebattery cell. Materials which provide the needed porosity include carbonblack, graphite, carbon fibers, carbon nanotubes, and other non-carbonmaterials. The pores of the cathode 370, separators 340, 360, 361,sensing sheet 350, and anode 330 are filled with an ionically conductiveelectrolyte that contains a salt such as lithium hexafluorophosphate(LiPF₆) that provides the electrolyte with an adequate conductivitywhich reduces the internal electrical resistance of the battery cell.The electrolyte solution enhances ionic transport within the batterycell. Various types of electrolyte solutions are available including,non-aqueous liquid electrolytes, ionic liquids, solid polymers,glass-ceramic electrolytes, and other suitable electrolyte solutions.

The anode current collector 320 and cathode current collector 380 areelectrically conductive materials that conduct electrons between theelectrode and electrode tabs of the cell. The materials of currentcollectors may also be efficient thermal conductors, which allow heatgenerated within the battery cell 300, 395 to be dissipated outside thebattery cell 300, 395. In some examples, the current collectors mayinclude various metals or carbon based materials. In some examples, thecurrent collectors may include graphite, aluminum, copper, gold,platinum, magnesium, or titanium. In various embodiments the currentcollector materials may be chosen such that the current collector tabs310 and 390 are resistant to potential deleterious effects caused byexposure to the atmosphere allowing the current collector tabs 310 and390 to act as electrical contacts external to the battery cell 395. Incertain embodiments the anode current collector 320 may be copper andthe cathode current collector 380 may be aluminum.

The separator 361 of FIG. 3B or first and second separators 340 and 360as described in FIG. 3A may comprise one or more electrically insulatingionic conductive materials. In some examples, the suitable materials forseparator 361 may include porous polymers, ceramics, and two dimensionalsheet structures such as graphene, boron nitride, and dichalcogenides.

An embodiment of a sensing sheet 400 is shown in FIG. 4. In the exampleof FIG. 4, the sensing sheet 400 includes sensing tabs 410, 420, and 430along the periphery of the sensing sheet 400. FIG. 4 also includes, ananode current collector tab 440 connected to an anode below the sensingsheet 400. In the illustrated example of FIG. 4, the sensing sheet 400has three sensing tabs 410, 420, and 430 along the periphery of thesensing sheet 400, however, a different number of additional sensingtabs may be used along the periphery of the sensing sheet 400 providedthe sensing tabs remain spatially separated from each other.

In an embodiment, the sensing sheet 400 and sensing tabs 410, 420, 430may be formed from a thin layer of an electrically conductive material.In some examples, the electrically conductive material may include ametal selected from a group consisting of copper, aluminum, titanium,platinum, gold, and combinations thereof. In one example, the sensingsheet 400 may be a single layer. In another example, the sensing sheet400 may be a multilayered sheet with combination of variousconductive/conductive material or conductive/non-conductive material. Inyet another example, the sensing sheet 400 may be a flexible sheet, afoldable sheet, or a combination thereof.

An embodiment of a battery system 500A is shown in FIG. 5A. The batterysystem includes an anode tab 510, an anode 520, a separator 530, sensingtabs 540A, 540B, and 540N (collectively “sensing tabs 540”), a cathode550, a cathode tab 560, sensing circuitry 570, and a battery managementsystem 580. In some embodiments the sensing tabs 540 may correspond tothe sensing tabs 410, 420, 430 illustrated as part of sensing sheet 400in FIG. 4.

In the example of FIG. 5A, the battery cell 502, the anode tab 510, theanode 520, the separator 530, the sensing tabs 540, the cathode 550, thecathode tab 560, and the sensing circuitry 570 correspond to the batterycell 100, the anode tab 110, the anode 120, the separator 130, thesensing tabs 140, the cathode 150, the cathode tab 160, and the sensingcircuitry 170, respectively, as described in FIG. 1. In contrast to FIG.1, in the example of FIG. 5A, system 500A further includes a batterymanagement system 580. Battery management system 580 is communicativelyconnected to the battery cell 502. In one example, the batterymanagement system 580 is electrically connected to the battery cell 502via electrical links (e.g., wires). In another example, the batterymanagement system 580 may be wirelessly connected to the battery cell502 via a wireless communication network. The battery management system580 may be for example a microcontroller (with memory and input/outputcomponents on a single chip or within a single housing) or may includeseparately configured components, for example, a microprocessor, memory,and input/output components. The battery management system 580 may alsobe implemented using other components or combinations of componentsincluding, for example, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field-programmable gate array(FPGA), or other circuitry. Depending on the desired configuration, theprocessor may include one more levels of caching, such as a level cachememory, one or more processor cores, and registers. The exampleprocessor core may include an arithmetic logic unit (ALU), a floatingpoint unit (FPU), or any combination thereof. The battery managementsystem 580 may also include a user interface, a communication interface,and other computer implemented devices for performing features notdefined herein may be incorporated into the system. In some example, thebattery management system 580 may include other computer implementeddevices such as a communication interface, a user interface, a networkcommunication link, and an interface bus for facilitating communicationbetween various interface devices, computing implemented devices, andone or more peripheral interfaces to the microprocessor.

The memory of the battery management system 580 may includecomputer-readable instructions that, when executed by the electronicprocessor of the battery management system 580, cause the batterymanagement system and, more particularly the electronic processor, toperform or control the performance of various functions or methodsattributed to battery management system 580 herein (e.g., detection ofan internal short from a dendrite formation, identification of dendritematerial, and/or mitigation of the internal short). The memory mayinclude any transitory, non-transitory, volatile, non-volatile,magnetic, optical, or electrical media, such as a random access memory(RAM), read-only memory (ROM), non-volatile RAM (NVRAM),electrically-erasable programmable ROM (EEPROM), flash memory, or anyother digital or analog media. The functions attributed to the batterymanagement system 580 herein may be embodied as software, firmware,hardware or any combination thereof. In one example, the batterymanagement system 580 may be embedded in a computing device and thesensing circuity 570 is configured to communicate with the batterymanagement system 580 of the computing device external to the batterycell 502. In this example, the sensing circuitry 170 is configured tohave wireless and/or wired communication with the battery managementsystem 580. For example, the sensing circuitry 570 and the batterymanagement system 580 of the external device are configured tocommunicate with each other via a network. In yet another example, thebattery management system 580 is remotely located on a server and thesensing circuitry 570 is configured to transmit data of the battery cell502 to the battery management system 580. In the above examples, thebattery management system 580 is configured to receive the data and sendthe data to an electronic device for display as human readable format.The computing device may be a cellular phone, a tablet, a personaldigital assistant (PDA), a laptop, a computer, a wearable device, orother suitable computing device. The network may be a cloud computingnetwork, a server, a wireless area network (WAN), a local area network(LAN), an in-vehicle network, a cloud computing network, or othersuitable network.

The battery management system 580 is configured to receive data from thesensing circuitry 570 including current, voltage, and/or resistancemeasurements. Battery management system 580 is also configured todetermine a condition of the battery cell 502. Based on the determinedcondition of battery cell 502, the battery management system 580 mayalter the operating parameters of the battery cell 502 to maintain theinternal structure of the battery cell 502. The battery managementsystem 580 may also notify a user of the condition of the battery cell502.

Another embodiment is shown in the example of FIG. 5B as a system 500B.The system 500B of FIG. 5B is similar to the system 500A of FIG. 5A,except, the sensing circuitry 570 is external to the battery cell 502.As illustrated in FIG. 5B, the sensing circuitry 570 is separate fromthe battery cell 502 and the battery management system 580. It should beunderstood that the specific type, number, and configuration of thecomponents, including sensing circuitry 570, are provided as examples insystems 500A and 500B in FIGS. 5A and 5B, respectively. In otherembodiments, the systems 500A and 500B in FIGS. 5A and 5B may includefewer or additional components in different combinations andconfigurations than illustrated in FIGS. 5A and 5B. For example, inother embodiments, the sensing circuitry 570 is part of the batterymanagement system 580, and the battery management system 580 is directlyconnected to the sensing tabs 540 within the battery cell 502.

An embodiment of a system 600 is shown in FIG. 6. In the example of FIG.6, the system 600 includes a battery cell 602, a sensing sheet 620,sensing sheet tabs 630, 640, and 650, an anode current collector tab660, a sensing circuitry 670, and a battery management system 680. Inthe example of FIG. 6, the battery cell 602, the sensing circuitry 670,and the battery management system 680 correspond to the battery cell502, the sensing circuitry 570, and the battery management system 580 asdescribed in FIGS. 5A and 5B.

The battery management system 680 uses the sensing circuitry 670 tocollect voltage and/or current data between the anode current collectortab 660 and the sensing sheet 620. For example, the sensing circuitry670 may individually measure the voltage and/or current between each ofthe sensing tabs 630, 640, and 650 and the anode current collector tab660. The measured parameters are then used by the battery managementsystem 680 to determine conditions within the battery cell 602.

To detect a dendrite formation, battery management system 680 can detectan electrical circuit formed between the sensing tabs 630, 640, and 650,and the anode current collector tab 660. The voltage V_(m) measuredbetween each sensing tab 630, 640, and 650 and the anode currentcollector tab 660, and the applied current I_(s) to anode currentcollector tab 660 can be used by the battery management system 680 todetermine additional information about the internal short. For example,the battery management system 680 may determine the position (e.g., atwo-dimensional position) and resistance of the dendrite. Upondetermination of the position and resistance, the battery managementsystem 680 may also identify the dendrite material based on thedetermined resistance. Identification of the dendrite material may allowthe battery management system 680 to perform additional actions (e.g.,actions to mitigate the potential effects of the dendrite within thebattery cell 602).

By determining the presence of a dendrite between the anode (not shown)and sensing sheet 620 prior to the dendrite penetrating through theseparator region and potentially forming an internal short between theanode and cathode of the battery corrective actions may be taken. Thebattery management system 680 may take various actions depending on thecomposition, number, and location of the detected dendrites. Forexample, if a dendrite is composed of lithium, the battery managementsystem 680 may cause or provide a current to flow through the dendritesufficient to raise the temperature of the dendrite above the meltingpoint of lithium, about 180 degrees Celsius, in order to melt andeliminate the internal short caused by the dendrite. If, the dendrite iscomposed of a higher melting material, such as copper, iron, nickel,chromium, cobalt, or manganese, the battery management system 680 mayadvise a user that the battery needs to be serviced. For example, thebattery management system 680 may advise a technician to replace aparticular battery cell (e.g., the battery cell 602). In this example,the battery management system 680 may also advise a technician that adendrite is forming and that the dendrite cannot be mitigated by thermaltreatment. In some examples, the battery management system 680, theuser, or the technician can initiate a shutdown protocol for the batteryallowing the battery to be serviced.

FIG. 6 illustrates a sensing sheet 620 having three sensing tabs 630,640, and 650 along the periphery of the sensing sheet 620, however,additional sensing tabs may be included provided the sensing tabs remainelectrically separate from each other.

Although the sensing circuitry 670 has been described herein asmeasuring electrical parameters between each of sensing tabs 630, 640,and 650 and anode current collector tab 660, the sensing circuitry 670may also be used to measure electrical parameters between each ofsensing tabs 630, 640, and 650 and a cathode current collector tab. Asimilar system to system 600 illustrated in FIG. 6 may be used to detectand identify internal shorts formed on the cathode. For example, theelectrolyte may contain additives that polymerize when the cathodereaches a high potential. The resulting polymer is slightly electricallyconductive and can create a highly resistive internal short through theseparator that may cause the battery management system 680 to shut downthe cell in a safe manner. A battery structure having a sensing sheet aspart of the separator region could potentially detect the formation ofsuch internal shorts and advise the user to replace the affected batterycell.

The resistance between the anode current collector tab 660 and each ofthe sensing tabs 630, 640, and 650 includes several components inseries. The first resistance component is the negative tab/negativecurrent collector contact resistance. The second resistance component isthe resistance in the negative electrode from the negative tab to theinternal short. The third resistance component is the internal shortresistance. The fourth resistance component is the resistance in thesensing sheet from the internal short to the sensing tab. The fifthresistance component is the sensing sheet/sensing tab contactresistance.

Welding at the sensing tabs 630, 640, and 650 is expected to minimizethe tab contact resistances, or, if significant, the contact resistancescan be measured a priori, whereas the resistance in the anode should bemuch lower than that in the sensing sheet 620. For example, compare atypical copper current collector thickness of 10 micrometers or more toa sensing sheet thickness of about 50 nm to 100 nm, which yields aresistance in the sensing sheet 620 that is on average two orders ofmagnitude higher than that in the anode. The resistances of typicaldendrites (e.g., a copper or lithium dendrites with about a 1-micrometerdiameter through a 25-micrometer separator) are roughly the same orderof magnitude of the resistance through the sensing sheet 620 (e.g.,50-nm thick sheet with 5-cm width and 5-cm length).

The battery management system 680 may perform the followingdeterminations as illustrated in FIG. 7 and as described below todetermine the resistance of the internal short 722 and its position onthe sensing sheet 720, which corresponds to the sensing sheet 620 asdescribed in FIG. 6. For ease of understanding, the followingdescription assumes all resistances other than the dendrite resistanceand the sensing sheet resistances are negligible. First, the batterymanagement system 680 may use the origin of the two dimensional space atone corner of the sensing sheet 720. Relative to the origin, theinternal short 722 is located at the unknown position (x₀, y₀), and thelocation of one of the sensing tabs 730 is at the known coordinate (x₁,y₁). The length and width of the sensing sheet 720 are L and W,respectively. The battery management system 680 may define a circle withradius r₀centered at (x₀, y₀) around the internal short 722 and asemicircle of radius r₁ centered at (x₁, y₁) around the sensing tab 730.In measuring the voltage V_(m) of the sensing circuit, a very smallcurrent i_(s) is applied such that the total DC resistance of thesensing circuit is obtained by dividing the measured voltage, V_(m), bythe applied current, i_(s), as defined by Equation 1.

R _(DC) =R _(S) +R _(ss) =V _(m) /i _(s)  (1)

In Equation 1, R_(S) is the resistance of the internal short 722 andR_(ss) is the resistance of the sensing sheet 720.

In the limits r₀→0 and r₁→0, the current density can be approximated asuniform in all directions normal to the circle as defined by Equation 2and semicircle as defined by Equation 3,

$\begin{matrix}\underset{\_}{\overset{\rightharpoonup}{i} = {\frac{i_{s}}{2\pi \; r_{0}d}\hat{n}}} & (2) \\{\overset{\rightharpoonup}{i} = {{- \frac{i_{s}}{\pi \; r_{1}d}}\hat{n}}} & (3)\end{matrix}$

In Equations 2 and 3, d is the thickness of the sensing sheet and{circumflex over (n)} is the unit normal with respect to the circle orsemicircle in the x-y plane. Written as components i_(x) and i_(y),Equations 2 and 3 can redefined as Equations 4 and 5 for the circle andsemicircle, respectively.

$\begin{matrix}{{i_{x} = {\frac{i_{s}}{2\pi \; r_{0}^{2}d}\left( {x - x_{0}} \right)}},\underset{\_}{i_{y} = {\frac{i_{s}}{2\pi \; r_{0}^{2}d}\left( {y - y_{0}} \right)}}} & (4) \\{{i_{x} = {{- \frac{i_{s}}{\pi \; r_{i}^{2}d}}\left( {x - x_{1}} \right)}},{i_{y} = {{- \frac{i_{s}}{\pi \; r_{1}^{2}d}}\left( {y - y_{1}} \right)}}} & (5)\end{matrix}$

In general, r₀<r₁<<W<L, the battery management system 680 can use theabove approximation in computing the voltage drop between the internalshort 722 and the sensing tab 730.

Within the region of the sensing sheet 720 that is outside the circleand semicircle, there are no additional current sources or sinks, andtherefore Laplace's equation holds as defined by Equation 6.

∇²ϕ=0   (6)

In Equation 6, ϕ is the potential in the sensing sheet 720. This isderived from the current balance as defined by Equation 7 and Ohm's lawas defined by Equation 8.

$\begin{matrix}\underset{\_}{{\nabla{\cdot \overset{\rightharpoonup}{i}}} = 0} & (7) \\{\overset{\rightharpoonup}{i} = {{- \sigma}{\nabla\; \varphi}}} & (8)\end{matrix}$

Both Equations 7 and 8 apply in the region of the sensing sheet 720outside the circle and semicircle. The battery management system 680 mayestablish an arbitrary reference voltage. For example, the batterymanagement system 680 may prescribe the reference voltage at the originas defined by Equation 9.

ϕ(0,0)=0   (9)

The voltage drop and effective resistance through the sensing sheet 720are defined by Equations 10 and 11.

V _(ss)=ϕ(x ₁ ,y ₁)−ϕ(x ₀ ,y ₀   (10)

R _(ss) =V _(ss) /i _(s)   (11)

Since the value of ϕ is not computed explicitly at these positions, thebattery management system 680 may approximate the potentials byaveraging the values of the potential at the respective peripheries ofthe circle and semicircle.

A variety of methods can be employed by the battery management system680 to solve the above set of equations to derive the effective sensingsheet resistance or voltage drop, provided the position and resistanceof the internal short 722 is known. In one example method, the batterymanagement system 680 may map the rectangular domain to thesemi-infinite domain via a Schwarz-Christoffel transformation, with thesolution to Laplace's equation derived in the semi-infinite domain, andthe battery management system 680 may map the solution back to therectangular domain. In another example method, the battery managementmay solve Laplace's equation in the rectangular domain via a separationof variables, which results in a series expansion solution in x and yfor the potential. In yet another example method, the battery managementsystem 680 may compute Laplace's equation numerically using finitedifference, finite volume, control volume, or other numerical methods.In another example method, as illustrated in FIG. 8, the batterymanagement system 680 may approximate the sensing sheet 720 as adiscrete network of resistors in two dimensions and solve the equationsthat result from Kirchoff's current and voltage laws.

Additionally, the position (x₀, y₀) and resistance (R_(S)) of theinternal short 722 can be determined from at least three independentmeasurements of the total DC resistance. The battery management system680 may measure the voltage drop between the anode tab and three or moreseparate sensing tabs along the periphery of the sensing sheet 720. Insome examples, if three different tabs exist at different locations onthe periphery, then the battery management system 680 can similarlyprovide three different measurements of the total sensing circuitresistance by alternately closing the circuit to each of the three tabs.In other examples, more than three different measurements may be used todetermine a unique solution to the set of variables (R_(S), x₀, y₀).

The battery management system 680 may measure the voltage of the sensingcircuit subject to an imposed current of known quantity, which is onetechnique for obtaining the values of the resistance and position of theinternal short 722. Additionally or alternatively, in some examples, theresistance of each sensing circuit may be measured by applying aspecified voltage and measuring the current.

A flowchart of the operation of an embodiment of the battery managementsystem 580 of FIG. 5 for the detection of an internal short is presentedin FIG. 9. FIG. 9 is described with reference to the system 500A of FIG.5A. The battery management system 580 receives an output from thesensing circuitry 570 indicative of a first voltage level (block 902).The battery management system 580 detects a change from the firstvoltage level to a second voltage level that is indicative of aninternal short within the sensing sheet (block 904). The batterymanagement system 580 determines the resistance and location of theinternal short within the sensing sheet (block 906). The batterymanagement system 580 identifies the material of the dendrite based onthe determined resistance of the dendrite (block 908). In some examples,the battery management system 580 may treat the internal short based onthe identified dendrite material (block 910).

A flowchart of the operation of an embodiment of the battery managementsystem 680 for the detection of an internal short is presented in FIG.10. FIG. 10 is described with reference to system 600 of FIG. 6. Thebattery management system 680 applies a current i_(s) and monitors afirst voltage level (V_(m1)) between the anode current collector tab 660and a first sensing tab 630 (block 1000). If the battery managementsystem 680 does not detect a change in the first voltage level (NO atdecision block 1002), then the battery management system 680 continuesto monitor the first voltage level (block 1000). However, if the batterymanagement system 680 detects that the first voltage level is less thana threshold voltage level (YES at decision block 1002), then the batterymanagement system 680 opens the circuit to the first sensing tab 630(block 1004). The battery management system 680 closes the circuit to asecond sensing tab 640, applies the current i_(s), and measures a secondvoltage level (V_(m2)) (block 1006). After measuring the second voltagelevel, the battery management system 680 opens the circuit to the secondsensing tab 640 (block 1008). The battery management system 680 closesthe circuit to a third sensing tab 650, applies the current i_(s), andmeasures a third voltage level (V_(m3)) (block 1010). Based on themeasured voltage levels and applied currents, the battery managementsystem 680 determines the resistance, Rs, and two-dimensional positioncorresponding to the internal short (block 1012). In some examples, thebattery management system 680 may determine a treatment based on thedetermined resistance, Rs, of the internal short.

The battery management system 680 determines whether the resistance (Rs)is below a threshold resistance. If the battery management system 680detects that the resistance (Rs) is above a threshold resistance (NO atdecision block 1014), the battery management system 680 either activatesa dendrite elimination protocol to eliminate the dendrite or monitor thefirst voltage level of the first sensing tab 630 (block 1018). In someexamples, the dendrite elimination protocol may include a currentthrough the internal short sufficient to heat the dendrite above themelting point of the dendrite. For example, the battery managementsystem 680 may identify the dendrite as a lithium dendrite, and thebattery management system 680 may pass a current through the lithiumdendrite that raises the temperature above 180 degrees Celsius to meltthe lithium dendrite. The applied current will also raise thetemperature of the parts of the sensing circuit through which thecurrent flows. In some embodiments, the circuit of the applied currentmay be alternated between different sensing tabs 630, 640, 650 in orderto limit the amount of heating of any given part of the sensing sheet620, while localizing the region of continuous heating to the internalshort itself. In some embodiments additional sensing tabs may be addedto further differentiate between the sensing sheet 620 and the internalshort when raising the temperature of the cell. The battery managementsystem 680 may activate the dendrite elimination protocol or continuemonitoring the first voltage level when there is no change in the firstvoltage level (NO at decision block 1020). However, the batterymanagement system 680 may deactivate the dendrite elimination protocoland restart the dendrite identification process when there is a changein the first voltage level (YES at decision block 1020).

If the battery management system 680 detects that the resistance (Rs) isbelow a threshold resistance (YES at decision block 1014), the batterymanagement system 680 activates a battery shutdown protocol. In someexamples, the resistance (Rs) of copper is below the predeterminedthreshold that will cause the battery management system 680 to activatethe battery shutdown protocol.

The embodiments described above have been shown by way of example, andit should be understood that these embodiments may be susceptible tovarious modifications and alternative forms. It should be furtherunderstood that the claims are not intended to be limited to theparticular forms disclosed, but rather to cover all modifications,equivalents, and alternatives falling with the spirit and scope of thisdisclosure.

It is believed that embodiments described herein and many of theirattendant advantages will be understood by the foregoing description,and it will be apparent that various changes may be made in the form,construction and arrangement of the components without departing fromthe disclosed subject matter or without sacrificing all of its materialadvantages. The form described is merely explanatory, and it is theintention of the following claims to encompass and include such changes.

What is claimed is:
 1. A battery comprising: an anode; a cathode; anelectrically insulating separator having a sensing sheet and locatedbetween the anode and the cathode, wherein the electrically insulatingseparator electrically insulates the anode from the cathode, and whereinthe sensing sheet includes three or more sensing tabs located at aperiphery of the sensing sheet; and sensing circuitry electricallyconnected to each of the three or more sensing tabs and configured todetermine at least one of a resistance, a current, or a voltage at eachof the three or more sensing tabs, and output an indication of the atleast one of the resistance, the current, or the voltage at each of thethree or more sensing tabs.
 2. The battery of claim 1, furthercomprising an anode current collector adjacent to the anode and an anodecurrent collector tab attached to the anode current collector.
 3. Thebattery of claim 1, further comprising a cathode current collectoradjacent to the cathode and a cathode current collector tab attached tothe cathode current collector.
 4. The battery of claim 1, wherein theelectrically insulating separator having the sensing sheet includes afirst electrically insulating separator and a second electricallyinsulating separator, and wherein the sensing sheet is located betweenthe first electrically insulating separator and the second electricallyinsulating separator.
 5. The battery of claim 1, wherein theelectrically insulating separator further comprises a porous polymericfilm between the sensing sheet and at least one of the cathode or theanode.
 6. The battery of claim 1, wherein the sensing sheet includes amaterial selected from a group consisting of copper, aluminum, titanium,platinum, and gold.
 7. A system comprising: a battery having an anode; acathode; an electrically insulating separator having a sensing sheet andlocated between the anode and the cathode, wherein the electricallyinsulating separator electrically insulates the anode from the cathode,and wherein the sensing sheet includes three or more sensing tabslocated at a periphery of the sensing sheet; and sensing circuitryelectrically connected to each of the three or more sensing tabs andconfigured to determine at least one of a resistance, a current, or avoltage at each of the three or more sensing tabs, and output anindication of the at least one of the resistance, the current, or thevoltage at each of the three or more sensing tabs; and a batterymanagement system communicatively connected to the battery andconfigured to receive the output from the sensing circuitry, anddetermine a resistance and a two-dimensional position of the internalshort on the sensing sheet based on the output from the sensingcircuitry.
 8. The system of claim 7, wherein the battery managementsystem is further configured to identify a material type of a dendritecausing the internal short based on the resistance of the internalshort.
 9. The system of claim 8, wherein the battery management systemis further configured to treat the internal short based on theidentification of the material type of the dendrite.
 10. The system ofclaim 9, wherein the battery management system is configured to treatthe internal short comprises the battery management system configured toactivate a battery shutdown protocol.
 11. The system of claim 9, whereinthe battery management system is configured to treat the internal shortcomprises the battery management system configured to activate adendrite elimination protocol.
 12. The system of claim 11, wherein thedendrite elimination protocol includes the battery management systemconfigured to provide a current through the internal short, and whereinthe current is sufficient to raise a temperature of the dendrite above amelting point of the material type of the dendrite.